ARMING SAFETY SWITCH MK 122 MOD 0

The Mk 122 Mod 0 arming safety switch (fig. 1-14) connects the fuze control circuits of the bomb in the aircraft to the electric fuze circuits in the bomb. This switch provides an open circuit and a RADHAZ shield to prevent electromagnetic radiation from entering the fuze circuits.

While the weapon is loaded, the coaxial cable of the switch is plugged into the receptacle of the aircraft's electrical arming unit. When the bomb is suspended from the rack, the lanyard is attached to a fixture on the rack or pylon. Upon bomb release, the lanyard pulls the lanyard pin and closes the fuze circuit. The lanyard is long enough so the weapon separates from the bomb rack suspension hooks before the lanyard pin is pulled from the switch. This ensures that the fuze does not receive charging voltages in case of weapon release failure. The coaxial cable is longer than the lanyard, which permits sufficient time for the charging voltage to pass from the electrical arming unit on the aircraft to the fuze electric circuits on the bomb before the cable is pulled free or breaks from the arming unit receptacle.

NOTE: The Mk 122 Mod 0 switch must be installed and removed in a RADHAZ-free environment.

MK 43 MOD 0 TARGET DETECTING DEVICE

The Mk 43 Mod 0 target detecting device (fig. 1-15) is a proximity variable time (VT) nose element that gives airburst capability for electric-fuzed Mk 80 (series) bombs.

The Mk 43 Mod 0 VT element is compatible with all electric tail fuzes and is identified by the dark green color of the nose cone. Its internal circuitry is powered by a thermal battery. The thermal battery is initiated by +300 volts dc or by the striker rod.

The Mk 43 is initiated mechanically (striker rod) only when a delay airburst is desired. This is the alternate method used to provide VT operation when the fuze is not initiated with the +300 volts dc. The conventional VT mode is selected by initiating the fuze with +300 volts dc. When the fuse is initiated with +300 volts dc, the Mk 43 operates automatically.

Figure 1-14.-Mk 122 Mod 0 arming safety switch.

Figure 1-15.-Mk 43 Mod 0 target detecting device.

The fuze circuitry produces a lobe pattern. It radiates a pattern at right angles (fig. 1-16) to the longitudinal axis of the weapon.

When the Mk 43 is initiated by the conventional method, fuze functioning occurs instantaneously when a firing pulse is received from the thermal battery. If the alternate method is used (striker rod), the fuze is set for either of the two functioning delays-DLY 1 for 0.015-second delay or DLY 2 for 0.100-second delay. Detonation of the bomb is delayed by either 0.015 second or 0.100 second, depending on the delay that is selected.

Figure 1-16.-Mk 43 Mod 0 target detecting device antenna pattern.

M20 AND M20A1 SENSING ELEMENT PROXIMITY FUZE

The M20 is identifiable by the tan color of its plastic nose cone. The nose cone of the M20A1 is brick red. The only difference between the two sensing elements (fig. 1-17) is the number of burst height ranges and the type of plastic employed in the nose cone. The sensing elements are not classified as a fuze because they do not contain an explosive train. They must be used with an impact tail fuze. The impact fuze provides the explosive train and safety for the combination. The sensing element can be activated by either an electrical signal or via the withdrawal of an arming wire from the striker rod release mechanism. Presently, the only method used for activation is mechanical. The sensing elements employ a longitudinal loop antenna (fig. 1-18). The burst height range is between 100 feet and 160 feet for the "HI" setting and between 20 feet and 60 feet for the "LO" setting. The M20A1 has only one range (equal to the M20 "LO" setting).